3 ms·

NULL is the lack of any string. If one view a string as a result of an operation, then an INVALID string is the consequence of bad input to an operation.

• saagarjha 7y ago
  Why can’t NULL serve as the invalid string in this case? It’s clearly not a valid string that an operation will return.
  • codehero 7y ago
    If you have studied Computer Science, you should know that the null string is quite a valid string. Let's take strstr, which finds a matching substring needle in a haystack string. -returns a NULL string if the needle is not in the haystack. -returns pointer to first matching substring. Extend strstr with VALIDITY Understood behaviour if both are valid. Say the haystack is INVALID...as the return value is NULL or a strict substring of haystack, should return INVALID. A poison haystack should poison dependent strings. Say the haystack is valid but the needle is INVALID...should return NULL. A valid string never contains an INVALID string as a subsequence.
    • saagarjha 7y ago
      Here's my behavior: strstr(NULL, /* valid string */) I can't find the needle in the haystack (actually, I can't find anything in the haystack. I can't find the haystack.) Thus I return NULL. strstr(/* valid string */, NULL) I can't find the needle in the haystack (actually, I wouldn't be able to find it: I don't know what I'm looking for.) Return NULL.
      • codehero 7y ago
        You're explanation is not inconsistent with my proposal, but you don't seem to grasp VALIDITY.